1. Field of Invention
The present invention relates to a piezoelectric oscillator, a manufacturing method thereof, and an electronic device.
2. Description of Related Art
Piezoelectric oscillators are widely used to obtain constant frequency signals in electric circuits. Japanese Examined Utility Model Registration Application Publication No. 5-16724 describes a related art piezoelectric oscillator 501 shown in FIG. 9. Note that FIG. 9(A) is a plan view partway through manufacturing, and FIG. 9(B) is a side cross-sectional diagram at a portion equivalent to the plane H—H in FIG. 9(A). With the piezoelectric oscillator 501 shown in FIG. 9(B), a piezoelectric resonator 510 is mounted on the lower face of a lead frame 530, an integrated circuit device (IC) 560 is mounted on the upper face of the lead frame 530, and a resin package 570 is formed so as to seal the entirety with resin. Note that the cylinder-type piezoelectric resonator 510 shown in FIG. 9 is formed by sealing a piezoelectric resonator element, wherein an excitation electrode has been formed on a piezoelectric plate, within a metal cylinder, and extracting an external lead 524, for conducting between the excitation electrode and the external lead 524, from the cylinder. On the other hand, the IC 560 forms an oscillating circuit.
FIG. 9(A) illustrates the state immediately before forming the resin package 570. A die pad 552 is disposed at the center of the lead frame 530, with the IC 560 mounted thereupon. Also, mounting leads 542 for mounting the piezoelectric oscillator 501 are disposed on the four sides of the die pad 552, with each being electrically connected to the IC 560 by wire bonding. The outer portions of the mounting leads 542 are bent downwards after formation of the resin package 570, thereby forming mounting terminals. Further, connection leads 532 for connecting the piezoelectric resonator 510 and the IC 560 are formed at the intermediate portion of the mounting leads 542 in the vertical direction in FIG. 9(A). External leads 524 of the piezoelectric resonator 510 are connected to the lower face of the connection leads 532, and the upper face of the connection leads 532 are connected to the IC 560 by wire bonding. Thus, the piezoelectric resonator 510 and the IC 560 are electrically connected. The same configuration is illustrated in Japanese Patent No. 2621828 as well.
Piezoelectric oscillators are used in communication devices, such as cellular telephones and the like, but demands for reduction in the size of cellular telephones and the like are intensifying. Accordingly, there is strong demand for reduction in size and thickness of piezoelectric oscillators, as well. As of recent, package-type (plane-mounted) piezoelectric resonators have been developed, wherein a piezoelectric resonator element is sealed within a package, and external electrodes for conducting between excitation electrodes of the piezoelectric resonator element and external electrodes are formed on the rear face of the package. The reason that package-type piezoelectric resonators have been developed to replace the cylinder-type piezoelectric resonator 510 shown in FIG. 9 is in response to the demand for reduction in size and thickness of piezoelectric oscillators.
Along with reduction in size of piezoelectric oscillators, the mounting terminals and the like for joining to mounting boards are also reduced in size. Accordingly, the smaller the piezoelectric oscillators become, the smaller the area of contact between the mounting terminals and the mounting board becomes, reducing the joining strength. Accordingly, in the event that the piezoelectric oscillator is mounted in a portable electronic device such as a cellular telephone or the like, there is an increased probability that dropping the device may result in the piezoelectric oscillator coming loose at the portion of contact with the mounting board due to the great shock. This also holds true for the joining portion between the resin making up the resin package, and the terminals of the lead frame. Accordingly, the smaller piezoelectric oscillators become, the greater the importance is to enhance the strength of joining as to the mounting board and the resin making up the resin package.
However, with the above-described piezoelectric oscillator, there is the problem that the planar size increases, since the connection leads need to be disposed at the intermediate portion of the mounting leads. Consequently, there is a limit to reduction in the size of the piezoelectric oscillator. Accordingly, the present invention reduces the size by reducing the planar size. Also, the present invention enhances joining strength. Further, the present invention enhances mounting strength.